1 entrance
The entrance of civil air defense basement includes entrance, vent and other openings (smoke exhaust, water supply and drainage, electrical openings, etc.). Among them, the entrance design is an important content in the entrance protection and structural design of civil air defense projects.
1. 1 stirrup spacing problem of anti-collapse scaffold beam 1) Frequently asked questions. The stirrup spacing of anti-collapse scaffold beam should be 150mm or more; 2) Principle analysis. From the point of view of protection, the roof of anti-collapse scaffolding bears two kinds of loads, one is the vertical equivalent static load caused by the collapse of houses, and the other is the horizontal equivalent static load caused by air shock waves. Considering the load of these two parts, the structural requirements of anti-collapse scaffold beam should be the same as those of other parts of the basement. According to article 4. 1 1.GB 50038—2005 Design Code of civil air defence basement 10, the stirrup spacing in the encryption area should not be greater than h0/4(h0 is the effective height of the beam section) and should not be greater than 5 times the diameter of the main reinforcement [3]. At the same time, according to the document 19991February 15, Beijing Stone God Expert Committee 1 [20 15], the anti-collapse scaffolding also needs to be designed according to corresponding seismic measures [4], which is also listed in Table 6. 3. Article 3 in Code for Seismic Design of Buildings (GB 5001-2010). 3) Design suggestions. For the anti-collapse scaffolding at the entrance and exit, the beam height of not less than 400 mm and the diameter of reinforcement not less than 20 mm should be adopted as far as possible. In order to cooperate with these adjustments, the column spacing of anti-collapse scaffolding can be appropriately increased.
1.2 Load value and structural requirements of the wall around the main entrance and exit of stairs 1) Frequently asked questions. The wall around the main entrance and exit of stairs does not consider the equivalent static load of civil air defense and related structural requirements; 2) Principle analysis. With the increasing demand of urban underground space, the location of civil air defense basement in underground space is also diverse. The diversity of underground space usage leads to the diversity of walls around stairs, and sometimes there are cases where non-civil air defense basement and civil air defense basement use stairs. For the wall adjacent to soil, it is difficult to calculate and determine the action time and magnitude of internal pressure (air shock wave) and external pressure (compression wave in soil) by simple method. For safety reasons, the code stipulates that the internal pressure can be ignored and the explosive dynamic load caused by compression wave in soil can be calculated [3]. For the wall adjacent to the ordinary basement, only the influence of air shock wave entering the main entrance and exit is considered; For the case that there is a hole in the common basement and stairs are used in the common basement and civil air defense basement, although the air shock wave will spread through the hole, it will not reduce the air shock wave load in the actual design process because there is no relevant test basis. 3) Design suggestions. Stairs mainly enter and exit the walls around the building. When it is in direct contact with soil, the total height of the wall is considered as the equivalent static load of civil air defense according to the external wall in soil. When adjacent to an ordinary basement, the equivalent static load is determined according to the empty wall regardless of whether there is a hole in the wall; The wall around the corresponding staircase main entrance and exit should meet the relevant structural requirements of civil air defense.
1.3 load derivation of steel structure protective sealed door 1) frequently asked questions. The equivalent static load acting on the door frame wall should be considered according to the relevant regulations of concrete protective sealing door; 2) Principle analysis. When the reinforced concrete protective sealing door commonly used in air defense basement enters the plastic state and reaches the ultimate resistance under the action of explosive dynamic load, its failure develops along the "plastic hinge line", so its calculation diagram can be a simply supported rectangular plate with four sides. However, the internal structure of steel civil air defense door is determined by the beam-slab system which mainly transmits force in the direction of force. Therefore, most of its load is transferred to the door frame wall corresponding to the main stress direction, while the door frame wall corresponding to the secondary stress direction only bears the equivalent static load transferred by the local beam and slab.
The design of 1.4 door frame wall has the problem of disharmony between peacetime and wartime conditions. The reinforcement and structure of the door frame wall are only considered according to wartime working conditions. 2) Principle analysis. Conventional door frame wall design is to divide a complete door frame into four retaining walls: upper, lower, left and right. According to different equivalent static loads of civil air defense, the reinforcement of each retaining wall is calculated. However, because it is positioned as the door frame wall of civil air defense doors, and these walls are often only available in civil air defense basements, designers often ignore its mechanical requirements as an ordinary basement. For example, it is often forgotten that the left and right retaining walls should be provided with edge members from the seismic perspective. The upper retaining wall is functionally a connecting beam, and the lower retaining wall is also the ground beam of the basement. 3) Design suggestions. In view of the incongruity between the stress and structure of the door frame wall as a civil air defense component and the stress and structure of the seismic component, it is suggested that the enclosure design should be based on the scope, reinforcement method, horizontal reinforcement and vertical reinforcement of the door frame wall and edge component when designing the left and right retaining walls. The upper retaining wall and coupling beam, and the lower retaining wall and ground beam adopt the same principle.
2 diffusion chamber
Vent is an important part of civil air defense basement, and its protection usually adopts the combination of blocking and diffusion, that is, the wave attenuation system with explosion-proof valve and diffusion chamber is used to reduce the pressure of shock wave. The rationality and safety of diffusion chamber design plays a decisive role in the design of air defense structure with vents.
2. The stress and unreasonable load values of various parts of the diffusion chamber are common problems in 1). In the structural design of civil air defense basement, the following situations often occur: except the wall between diffusion chamber and shaft, other walls are only designed as closed walls; The equivalent static load of each part of the diffusion chamber is not considered or taken improperly. 2) Principle analysis. As shown in fig. 3, the diffusion chamber is a room that uses the internal space to weaken the incident shock wave energy. When the shock wave enters the diffusion chamber with large cross-section and certain volume from the entrance with small cross-section, the high-pressure gas rapidly diffuses and expands, so that its density and pressure decrease, thus ensuring that the residual pressure is less than the allowable pressure of the subsequent equipment.
The wall between the shaft and the diffusion chamber is the front wall of the diffusion chamber, and its outer side (shaft side) bears the empty wall load from the shaft, and its inner side (diffusion chamber side) bears the residual pressure load of the shock wave entering the diffusion chamber through the hanging plate valve. The top plate, bottom plate and outer wall of diffusion chamber in contact with soil bear residual pressure on the inner side and equivalent static load of civil air defense caused by compression wave in soil on the outer side. Because of the residual pressure, the structures in the soil usually have only cracks and will not collapse inward, so these components only bear the static load equivalent to civil air defense caused by compression waves in the soil.
2.2 Improper selection of hanging plate valve 1) Common problems. Regardless of the applicable conditions of the residual pressure of the diffusion chamber (for different doors and different diffusion chamber sizes), the diffusion chamber can only be selected according to the equivalent static load in the design scheme in Section 2. Above 1. It is common for buildings to choose HK series civil air defense doors in Grade A and Grade VI civil air defense basements. 2) Principle analysis. A very important parameter of hanging plate valve is the valve closing time. Closing time refers to the closing time when the overpressure (Δ PT) acting on the valve is equal to the valve design resistance (Δ PS). When the predetermined overpressure acting on the valve is greater than the design resistance of the valve, the valve will be destroyed; If the former is too small, the valve closing time will increase and the wave attenuation rate will decrease. Hanging plate valves commonly used in civil air defense basement engineering are HK series and BMH series, and the design resistance grade of HK series is only Grade 5. The design resistance grades of BMH series have corresponding grades 5 and 6. When HK series is used in Grade A and VI civil air defense basements, there will be cases where the predetermined overpressure on the door is less than the design resistance of the valve. At this time, the closing time of the valve will be longer, and the attenuation rate of the wave will decrease, resulting in an increase in the residual pressure in the diffusion chamber. If the diffusion chamber is still designed according to the values given in Section 2. 1, there will be safety problems, and the equipment connected to the diffusion chamber may be damaged by exceeding the allowable residual pressure. 3) Design suggestions. In view of the possible impact of this situation on the air defense basement, it is suggested to communicate with the building in time during the design process and ask it to adopt BMH series hanging plate valves suitable for class 6 in the air defense basement (when the air volume is less than 14 500 mm2); In view of the fact that only HK series hanging trapdoors can be used in some places, it is necessary to adjust the size of diffusion chamber according to clause F.0.3 [3] of GB50038—2005, so as to keep the residual pressure within the allowable range.
2.3 Insufficient protective thickness of front wall of diffusion chamber 1) Frequently asked questions. As shown in Figure 4, the thickness of B in the cross section of the front wall of the diffusion chamber is 200mm 2. According to article 4. 1 1.GB 50038—2005 Article 3 stipulates that the minimum thickness of the reinforced concrete air defense basement wall is 250 mm The front wall of the diffusion chamber is the wall between the shaft and the diffusion chamber, which bears the empty wall load from the shaft. Therefore, the thinnest part of the wall (marked B in the drawing) shall meet the requirements of this article.
3) Design suggestions. The thickness b of the front wall part of the diffusion chamber is greater than or equal to 250 mm.
The structural design of civil air defense basement is very different from that of ordinary basement, not only because the civil air defense load it bears is an instantaneous dynamic load that suddenly accelerates unloading, but also because the structural design is closely related to the requirements of architecture, ventilation and protection. Exploring the protection principle behind structural provisions is particularly important for designing economic, reasonable and safe civil air defense projects.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd